Gregory Lecrivain

Using reverse engineering and computational fluid dynamics to investigate a lower arm amputee swimmer's performance.

In front crawl swimming, the hand and the corresponding forearm generate major propulsive forces. Such forces have been studied largely through experimental tests and more recently through the use of steady computational fluid dynamics (CFD). However, the effect of the upper arm on the propulsive forces has generally not been taken into consideration. An understanding of such forces is fundamental for the performance of swimmers who have an arm amputation at the level of the elbow. This study introduces the great potential offered by the multidisciplinary approach combining reverse engineering and unsteady CFD in a novel dynamic and interactive way. A complex CFD mesh model, representing the swimmer body and its upper arm, is produced. The model, including the arm rotation and a body roll movement, interacts dynamically with the fluid flow. Forces generated by the upper arm can then be investigated in great detail. In this particular study, it is found that the upper arm effectively contributes to the propulsion of the body. The propulsive force was numerically computed throughout the pull and reaches maxima of 8 N. Results obtained in this study could be extended in a similar way to any other limb movement within a fluid flow.

Influence of the Lagrangian Integral Time Scale Estimation in the Near Wall Region on Particle Deposition

In a high temperature pebble-bed reactor core where thousands of pebbles are amassed, the friction between the outer graphite layer of the fuel elements triggers the formation of carbonaceous dust. This dust is eventually conveyed by the cooling carrier phase and deposits in the primary circuit of the high temperature reactor. The numerical prediction of carbonaceous dust transport and deposition in turbulent flows is a key safety issue. Most particle tracking procedures make use of the Lagrangian integral time scale to reproduce the turbulent dispersion of the discrete phase. In the present Lagrangian particle tracking procedure, the effect of the Lagrangian integral time scale near the wall is thoroughly investigated. It is found that, in the linear sublayer, a value of the normalized wall normal component of the Lagrangian integral time scale lower that 4 delivers accurate particle deposition velocities. The value worked out here near the wall region is in accordance with Lagrangian integral time scales derived from recent direct numerical simulations.

Effect of body roll amplitude and arm rotation speed on propulsion of arm amputee swimmers

Only a limited amount of research has gone into evaluating the contribution made by the upper arm to the propulsion of elite swimmers with an amputation at elbow level. With assistance of computational fluid dynamics (CFD) modelling, the swimming technique of competitive arm amputee swimmers can be assessed through numerical simulations which test the effect of various parameters on the effectiveness of the swimming propulsion. This numerical study investigates the effect of body roll amplitude and of upper arm rotation speed on the propulsion of an arm amputee swimmer, at different mean swimming speeds. Various test cases are simulated resulting in a thorough analysis of the complex body/fluid interaction with a detailed quantitative assessment of the effect of the variation of each parameter on the arm propulsion. It is found that a body roll movement with an amplitude of 45 degrees enhances greatly the propulsive contribution from the upper arm with an increase of about 70% in the propulsive force compared to the no roll condition. An increase in the angular velocity of the upper arm also leads to a concomitant increase in the propulsive forces produced by the arm. Such results have direct implications for competitive arm amputee front crawl swimmers and for those who coach them. One important message that emerges in this present work is that there exists, for any given swimming speed, a minimum angular velocity at which the upper arm must be rotated to generate effective propulsion. Below this velocity, the upper arm will experience a net resistive drag force which adversely affects swimming performance.

Creation of Body Surfaces From Reverse-Engineered Components

In the automotive industry or in similar industries, body panels need to be perfectly smooth for visual and aerodynamic reasons. In some cases, the component is a hand-made body part that will require a suitable CAD model for further development and manufacturing. Such a smooth CAD model can only be produced through reverse-engineering and CAD procedures that will make use of accurate surface reconstruction. This paper describes a reverse-engineering procedure for the production of a suitable CAD mesh from which surface reconstruction can take place. It then analyzes and compares three approaches assessing the continuity and the quality of each set of NURBS patches: automatic, semiautomatic, and completely manual surfacing. Recommendations are made for each method when creating CAD surfaces. Finally, a procedure is suggested to optimize the time and the quality of the final CAD model.

Direct numerical simulation of a particle attachment to an immersed bubble

A numerical extension of the “smooth profile method” is presently suggested to simulate the attachment of a colloidal particle to the surface of an immersed bubble. In this approach, the two fluid-particle boundaries and the fluidic boundary are replaced with diffuse interfaces. The method is tested under various capillary numbers. Upon attachment to a stable bubble, it is found that the method is capable of reproducing the three microprocesses associated with the particle attachment. The change in the trajectory as the particle approaches the fluidic interface, the collision process, and the sliding down the bubble surface are all captured. Potential application of the present method shows great promise in the field of froth flotation, where the capture of hydrophobic particles by rising bubbles is of primary importance.

Direct numerical simulation of an arbitrarily shaped particle at a fluidic interface

A consistent formulation is presented for the direct numerical simulation of an arbitrarily shaped colloidal particle at a deformable fluidic interface. The rigid colloidal particle is decomposed into a collection of solid spherical beads and the three-phase boundaries are replaced with smoothly spreading interfaces. The major merit of the present formulation lies in the ease with which the geometrical decomposition of the colloidal particle is implemented, yet allows the dynamic simulation of intricate three-dimensional colloidal shapes in a binary fluid. The dynamics of a rodlike, a platelike, and a ringlike particle are presently tested. It is found that platelike particles attach more rapidly to a fluidic interface and are subsequently harder to dislodge when subject to an external force. Using the Bond number, i.e., the ratio of the gravitational force to the reference capillary force, a spherical particle with equal affinity for the two fluids breaks away from a fluidic interface at the critical value Bo=0.75. This value is in line with our numerical experiments. It is here shown that a plate and a ring of equivalent masses detach at greater critical Bond numbers approximately equal to Bo=1.3. Results of this study will find applications in the stabilization of emulsions by colloids and in the recovery of colloidal particles by rising bubbles.